PURPOSE: To provide feasibility for getting a safe fuel cell power generation plant by injecting purge gas into the system of a fuel cell plant in a short time, without any non-reacted gas remaining in the system in case of an emergency of the plant by means of a shut off valve provided on the exit side of the recycle blower of a recycle line.

CONSTITUTION: In the state of power generation, the concentration of gas supplied to the fuel cell body 11 is made low in a low load zone. Accordingly, cut-off valves 34, 35 in a recycle line are kept opened due to the judgement function of a controller 36 receiving 'Blower Operation Signal' as soon as the start of operation of recycle blowers 15, 24, and flow in both recycle lines 14, 23 are confluent with the main line from a fuel control valve 12 and fed into the fuel cell body 11. In a high load range, the recycle blowers 15, 24 stop their operation, but 'close signal' is generated and transmitted to cut-off valves 34, 35 provided in recycle lines 14, 23 respectively. Accordingly, these valves come in closed state, causing only main line flow coming out of a fuel control valve 12 to be supplied to the fuel cell main body 11. Then, reverse flow of gas inside recycle lines 14, 23 is prevneted since cut-off valves 34, 35 are in closed state.